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    <meta charset="UTF-8" />
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    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
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  <body>
    <!-- 打印出1000-2000年中所有的闰年，并以每行四个数的形式输出 -->

    <script>
      for (var a = 1000; a <= 2000; a++) {
        if ((a % 4 == 0 && a % 100 != 0) || a % 400 == 0) {
          document.write(a + "<br>");
        }
      }
    </script>
  </body>
</html>
